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Acclimation processes by daily exercise stints at temperate conditions followed by short heat exposures.

In order to improve the conventional procedures for heat acclimation by making the process shorter and more efficient, four daily regimes of 30 minutes of exercise under temperate ambient conditions followed by a 30 minute walk under hot dry ambient conditions were administered to three groups of subjects. The respective exercise part for each group was as follows: 30 minutes of descent on a laddermill (negative work); 30 minutes of ascent on a laddermill (positive work); and 15 minutes of descent followed by 15 minutes of ascent on the laddermill. The four daily regimes of exercise and heat exposure were followed by four consecutive daily walks of up to 120 minutes in dry heat. A fourth control group was not subjected to the special acclimation regimen, but underwent the eight daily conventional acclimation procedures. Acclimation was judged by the increase in tolerance time for the walk in the heat and decrease in heart rate, rectal temperature and mean skin temperature. Partial acclimation was observed after the 4 days of the regimen for the three experimental groups and the 4 days of the conventional procedure on the fourth control group. The final state of acclimation was apparent on the eight day for all four groups. When the partial acclimation after the 4 day regimen was compared with the final state of acclimation, the following improvements were observed: 90 percent increase in tolerance time; 72 percent decrease in heart rate; 56 percent decrease in rectal temperature, and 45 percent fall in mean skin temperature. These improvements were similar to those observed after the 4 days of the conventional treatment on the control group as well as to those reported by others. (Grant No. R01-OH-00583)